1. Field of the Invention
The invention relates to a crankshaft for use with a variable compression engine.
2. Background Art
A xe2x80x9ccompression ratioxe2x80x9d of an internal combustion engine is defined as the ratio of the volume in a cylinder above a piston when the piston is at bottom-dead-center (BDC) to the volume in the cylinder above the piston when the piston is at top-dead-center (TDC). In general, the higher the compression ratio (hence, the expansion ratio), the higher the thermal efficiency of the engine. This in turn results in improved fuel economy and a higher ratio of output energy versus input energy of the engine.
In conventional internal combustion engines, however, the compression ratio is fixed and cannot be changed to yield optimal performance. Accordingly, variable compression ratio (VCR) internal combustion engines have been developed to vary the clearance volume of a cylinder in order to achieve improved fuel economy and increased engine power performance. Such VCR engines may be designed to have a higher compression ratio during low load conditions, and a lower compression ratio during high load conditions.
One known apparatus is disclosed in U.S. Pat. No. 5,146,879. This apparatus includes an eccentric sleeve that is used to vary the effective length of a connecting rod coupled to a crankshaft. The apparatus also includes a lock device capable of fixing rotation of the eccentric sleeve in a desired position, and a fluid pressure drive system for controlling operation of the lock device. Fluid from the drive system is supplied through the crankshaft, then through apertures in a bearing disposed about the crankshaft, and into the lock device. The apertures in the bearing, however, reduce effective bearing surface for lubrication.
The present invention addresses the shortcomings of the prior art by providing a crankshaft that is configured to supply pressurized fluid to an engine so as to effect a change in compression ratio of the engine, without requiring apertures to be formed in an associated rod bearing for fluid transmission.
Under the invention, a crankshaft is provided for use with a variable compression ratio engine having a connecting rod and a rod bearing associated with the connecting rod. The crankshaft includes a crankpin adapted to be coupled to the connecting rod with the rod bearing disposed between the crankpin and the connecting rod. The crankpin includes a circumferential surface having first and second side surface portions and a main surface portion disposed between the side surface portions. The main surface portion is configured to receive the rod bearing. The first side surface portion has a first aperture that is disposed at least partially outwardly of the rod bearing when the rod bearing is received on the main surface portion of the crankpin and the crankpin is coupled to the connecting rod. The crankpin further defines, at least partially, a first fluid passage in fluid communication with the first aperture for supplying pressurized fluid to the first aperture, such that the fluid is useable to vary compression ratio of the engine.